Figures for Chapter 5 Earmolds and earshells Dillon (2001) Hearing Aids

Figures for Chapter 5

Earmolds and earshells

Dillon (2001)

Hearing Aids

Figure 5.1 Cross sections of (a) a full concha earmold with a wide vent and (b) a Janssen mold that would have extremely similar acoustical properties, but different retention properties. See also Figure 5.3 for perspective views of these molds.

(a) (b)

Source: Dillon (2001): Hearing Aids

Hearing aid vent paths

Figure 5.2 Side view and cross section of the external ear, drawn to average full-size dimensions and typical shape (Salvinelli et al., 1991; Staab, 1999), and the names given to various parts of the ear (Shaw, 1975).

SAGGITAL SECTION(Lateral view)

POSTERIOR

ANTERIOR

Helix

Tragus

Eardrum

First bendSecond bend

AXIAL OR TRANSVERSE

SECTION (Superior view)

CORONAL OR FRONTAL SECTION

(Anterior view)

Tragus

Inter-tragalnotch

Anti-tragus

Lobule

Cavum-concha

Cymba-concha

Crus-helias

Anti-helix

SUPERIOR

INFERIOR

MEDIALLATERAL

Eardrum

Bone


The external

ear

Figure 5.3 Names given to various parts of an earmold or ear shell, based in part on Alvord, Morgan & Cartright (1997).

Canal stalk

Helix lock or top lock

Aperturicseal

Medial tubing aperture

Conchalrim

Tragal notchInter-tragal

ridge

Crural

groove

Anti-tragal notchFirst

bend

Soundbore


The earmold

“Standard” mold

Free FieldJanssen Sleeve

Figure 5.4 Earmold styles for BTE hearing aids.

Semi-skeletonSkeletonCarved shell

Canal lock Canal Hollow Canal

CROS - A CROS - B CROS - C


Earmold styles

Figure 5.5 Two types of elbows used in BTE earmolds. In (a) the tubing fits around the elbow, which creates some constriction. In (b) the tubing fits inside the elbow.

(a)

(b)


Earmold elbows

ITE

Low- profile

ITE ITC CIC

Figure 5.6 Axial view of typical placements for ITE, low-profile ITE, ITC and CIC hearing aids.


Custom aid styles

250 500 1000 2000 4000 8000125

Frequency (Hz)

Vents

Dampers Soundbore

Figure 5.7 Frequency regions affected by each of the components of the hearing aid coupling system.


Acoustic modifications

L2

L1

d1

d2

Figure 5.8 A vent made up of two tubes of different lengths and diameters.


Stepped-diameter vent

Figure 5.9 The inserts (larger than life-size) from a vent insert system, and the earmold and vent receptacle (approximately life-size) into which they fit. Positive Venting Valve (PVV) and Select-A-Vent (SAV) are two such systems commercially available.


Vent inserts

-30

-20

-10

0

250 500 1000 2000 40000Frequency (Hz)

Ve

nt

effe

ct (

dB

)

Tube

2 mm1 mm

Occluded

3.5 mm

Figure 5.10 Effect of different sized vents on the frequency response of amplified sound, relative to the response with a tightly fitting earmold or earshell (Dillon, 1985).


Low frequency vent-induced cuts

-30

-20

-10

0

125 250 500 1k 2k 4k 8k

Frequency (Hz)

Ven

t ins

ertio

n ga

in (

dB)

Occluded

1 mm2 mm

tube

3.5 mm

Figure 5.11 Insertion gain of the vent-transmitted sound path for vents of different sizes in an earmold or shell with a mean canal stalk length of 7 mm (Dillon, 1985). Also known as Real-Ear Occluded Gain.


Insertion gain of vent

Figure 5.12 Sound travels from a source to the eardrum via the amplified path (solid line) and the vent or leakage path (dashed line). An ITE is shown but the same principle holds for BTE or body aids.

Source


Multi-path propagation

-20

-10

0

10

20

30

125 250 500 1k 2k 4k 8kFrequency (Hz)

Inse

rtio

n ga

in (

dB)

Combined path

Amplifiedpath

Ventpath

Figure 5.13 Insertion gain of the vent-transmitted path and the amplified path and the way these might combine to form the insertion gain of the complete hearing aid.


Combined amplified and vent-transmitted sound paths

-20

-10

0

10

20

30


Inse

rtio

n ga

in (

dB)

0 degrees

120 degrees170

Figure 5.14 Insertion gain of the combined response for phase differences of 0, 120, and 170 degrees between the vent-transmitted and amplified sound paths shown in Figure 5.12. The combined path in Figure 5.12 assumed a phase difference of 90 degrees.


Phase and the combined insertion gain

-5

0

5

10

15

0 5 10 15 20

Length of canal stalk (mm)

Occ

lusi

on e

ffect

(dB

)

Figure 5.15 Increase in ear canal SPL (relative to no earmold) for the octave centered on 315 Hz when an aid wearer talks. Ear canal length was measured from the ear canal entrance along the center axis of the ear canal. For this person, the transition from cartilaginous to bony canal, as evidenced by the texture of the impression surface, commenced 9 mm into the canal (on the posterior wall, at the second bend) and completed 16 mm into the canal (on the anterior wall).


Occlusion SPL and canal stalk length

-20-15-10

-505

101520


Occ

lusi

on

eff

ect

(d

B) Occluded 1 mm

Tube

3.5 mm2 mm

Figure 5.16 The mean increase in SPL (relative to no earmold) in the ear canal for 10 subjects, as they talked while wearing earmolds with vents of different sizes (May & Dillon, 1992).


Vent size and occlusion SPL

A

Figure 5.17 Axial view of earmolds or shells that produce a very strong occlusion effect (A), and a very weak occlusion effect (B). The mold or shell shown in (C) will produce a weak occlusion effect and will also have minimal leakage of sound from the hearing aid. In each case, the wavy lines show the vibrating anterior wall and the arrow shows the primary direction in which bone conducted sound will travel once it enters the ear canal. The looseness of fit in each diagram has been exaggerated for clarity.

B C


Occlusion sound and mold/shell shape

Figure 5.18 Cross section of a Y-vent (or diagonal vent) in a BTE earmold.


Y-vent

do

l

di

l

do

di

Figure 5.19 Two acoustic horns, one stepped and one continuous, each with inlet diameter di, and outlet diameter do, and the boost (an increase in gain and maximum output) given to the frequency response by the continuous horn.

Frequency

Hor

n ef

fect

(dB

)

fh

i

o

d

dlog20


Acoustic horns

Figure 5.20 A Libby 4 mm horn (a) fully inserted into the earmold, and (b) partially inserted, with the mold forming the final section of the horn. Diameters are in mm.

43

2

(a)

43

2

(b)


Libby horn insertion

-4

-2

0

2

4

6

8

10

125 250 500 1 k 2 k 4 k 8 kFrequency (Hz)

Effe

ct o

f wid

e bo

re (

dB)

2

14

11

8

5

Figure 5.21 The effect of drilling a 4 mm diameter hole at the medial end of an earmold, relative to a constant 2 mm diameter sound bore. The number next to each curve shows the length, in mm, of the widened bore.


Effect of horn length

1.5 LP

1.35

14

1.9 mm

1.0

1.9 mm

13

0.9

1.5 mm

12

6C106C5

Figure 5.22 The dimensions of the constriction configurations known as 6C5, 6C10, and 1.5 LP (Etymotic Research Catalog; Killion, 1981).


Constrictions for high-frequency cuts

Hea

ring

thre

shol

d (d

B H

L)

250125 500 1k 2k 4k 8k

0

20

40

60

80

100

120

Frequency (Hz)

ER12-1

250125 500 1k 2k 4k 8k

0

20

40

60

80

100

120

ER12-2

250125 500 1k 2k 4k 8k

0

20

40

60

80

100

120

ER12-3

250125 500 1k 2k 4k 8k

0

20

40

60

80

100

120

ER12-4

Figure 5.23 Audiometric configurations for which each of the special earhooks has been designed. The hatched area in the ER12-3 audiogram is applicable if a non-occluding earmolds is used and the solid area if an occluding earmold is used.


Audiograms for special earhooks

10

20

30

40

100 1000 10000

Frequency (Hz)

Cou

pler

gai

n (d

B)

500200 2000 5000

No damper

1500 ohms at tip

1500 ohms at nub

Figure 5.24 Frequency response of a hearing aid with no damper, and with a 1500 ohm damper placed at each end of the earhook.


Effects of dampers

(a) (b)

Figure 5.25 An unmodified vent (a) and a shortened vent (b). The dashed lines in (a) indicate the position of the vent. The dashed lines in (b) indicate potential further stages of shortening, and the dotted line indicates the original profile.


Shortening the vent

(a)

(b)

Figure 5.26 Insertion of tubing into an earmold by (a) pushing, or by (b) pulling with a loop of wire.


Re-tubing

Documents

Figures for Chapter 5 Earmolds and earshells Dillon (2001) Hearing Aids